The present invention relates to techniques for eliminating reflections from optical systems such as gun sights, in order to prevent optical detection of the presence of such systems.
A technique presently employed to detect the presence and location of enemy troops is the detection of retroreflected light energy. Specifically, a beam of light energy, preferably in the invisible infra-red region of the spectrum, is scanned across an area to be searched. If the scanning beam impinges upon an optical system, such as a gun sight or the like, the beam will be retroreflected from a focal plane in that system back to the energy source. Detection of the retroreflected beam back at the source provides a means of locating enemy installations. This detection technique is diagrammatically illustrated in FIG. 1 wherein an optical system is represented by a lens 10 and focal plane 11. A viewer's eye or other reflective surface is considered to be located at the focal plane. The source of a light beam 12 is spaced sufficiently from lens 10 to be considered located at infinity relative to the lens. Consequently, beam 12 is focused at a point P in focal plane 11. The focal plane reflects the focused light in the form of reflected beam 13 which is imaged at infinity by lens 10. It is the detection of reflected beam 13 which indicates the presence of the illustrated optical system back at the source of beam 12.
The present invention has as its primary object the elimination of reflected beam 13 so that optical detection can be avoided.